Structure and formation method of semiconductor device with metal gate stack

ABSTRACT

A semiconductor device structure and the fabrication method are provided. The semiconductor device structure includes a first channel structure and a second channel structure over a substrate. The second channel structure is longer than the first channel structure. The semiconductor device structure also includes a first gate stack over the first channel structure, and the first gate stack has a first width. The semiconductor device structure further includes a first gate spacer extending along a sidewall of the first gate stack. In addition, the semiconductor device structure includes a second gate stack over the second channel structure and a second gate spacer extending along a sidewall of the second gate stack. The second gate stack has a portion extending along the second gate spacer, and the portion of the second gate stack has a second width. Half of the first width is greater than the second width.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapidgrowth. Technological advances in IC materials and design have producedgenerations of ICs. Each generation has smaller and more complexcircuits than the previous generation.

Over the course of IC evolution, functional density (i.e., the number ofinterconnected devices per chip area) has generally increased whilegeometric size (i.e., the smallest component (or line) that can becreated using a fabrication process) has decreased. This scaling-downprocess generally provides benefits by increasing production efficiencyand lowering associated costs.

However, these advances have increased the complexity of processing andmanufacturing ICs. Since feature sizes continue to decrease, fabricationprocesses continue to become more difficult to perform. Therefore, it isa challenge to form reliable semiconductor devices at smaller andsmaller sizes.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It shouldbe noted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1A-1B are top views of various stages of a process for forming asemiconductor device structure, in accordance with some embodiments.

FIGS. 2A-2D are cross-sectional views of various stages of a process forforming a semiconductor device structure, in accordance with someembodiments.

FIGS. 3A-3Q are cross-sectional views of various stages of a process forforming a semiconductor device structure, in accordance with someembodiments.

FIGS. 4A-4C are cross-sectional views of various stages of a process forforming a semiconductor device structure, in accordance with someembodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

The term “substantially” in the description, such as in “substantiallyflat” or in “substantially coplanar”, etc., will be understood by theperson skilled in the art. In some embodiments the adjectivesubstantially may be removed. Where applicable, the term “substantially”may also include embodiments with “entirely”, “completely”, “all”, etc.Where applicable, the term “substantially” may also relate to 90% orhigher of what is specified, such as 95% or higher, especially 99% orhigher, including 100%. Furthermore, terms such as “substantiallyparallel” or “substantially perpendicular” are to be interpreted as notto exclude insignificant deviation from the specified arrangement andmay include for example deviations of up to 10 degrees in someembodiments. The word “substantially” does not exclude “completely” e.g.a composition which is “substantially free” from Y may be completelyfree from Y in some embodiments.

Terms such as “about” in conjunction with a specific distance or sizeare to be interpreted so as not to exclude insignificant deviation fromthe specified distance or size and may include for example deviations ofup to 10% in some embodiments. The term “about” in relation to anumerical value x may mean x±5 or 10% in some embodiments.

Embodiments of the disclosure may relate to FinFET structure havingfins. The fins may be patterned using any suitable method. For example,the fins may be patterned using one or more photolithography processes,including double-patterning or multi-patterning processes. Generally,double-patterning or multi-patterning processes combine photolithographyand self-aligned processes, allowing patterns to be created that have,for example, pitches smaller than what is otherwise obtainable using asingle, direct photolithography process. For example, in someembodiments, a sacrificial layer is formed over a substrate andpatterned using a photolithography process. Spacers are formed alongsidethe patterned sacrificial layer using a self-aligned process. Thesacrificial layer is then removed, and the remaining spacers may then beused to pattern the fins. However, the fins may be formed using one ormore other applicable processes.

Embodiments of the disclosure may relate to the gate all around (GAA)transistor structures. The GAA structure may be patterned using anysuitable method. For example, the structures may be patterned using oneor more photolithography processes, including double-patterning ormulti-patterning processes. In some embodiments, double-patterning ormulti-patterning processes combine photolithography and self-alignedprocesses, allowing patterns to be created that have, for example,pitches smaller than what is otherwise obtainable using a single, directphotolithography process. For example, in some embodiments, asacrificial layer is formed over a substrate and patterned using aphotolithography process. Spacers are formed alongside the patternedsacrificial layer using a self-aligned process. The sacrificial layer isthen removed, and the remaining spacers may then be used to pattern theGAA structure.

Some embodiments of the disclosure are described. Additional operationscan be provided before, during, and/or after the stages described inthese embodiments. Some of the stages that are described can be replacedor eliminated for different embodiments. Additional features can beadded to the semiconductor device structure. Some of the featuresdescribed below can be replaced or eliminated for different embodiments.Although some embodiments are discussed with operations performed in aparticular order, these operations may be performed in another logicalorder.

FIGS. 2A-2D are cross-sectional views of various stages of a process forforming a semiconductor device structure, in accordance with someembodiments. As shown in FIG. 2A, a semiconductor substrate 100 isreceived or provided. The semiconductor substrate 100 has a first region10 and a second region 20. In some embodiments, one or more shortchannel (SC) devices are to be formed over the first region 10. One ormore long channel (LC) devices are to be formed over the second region20. In some embodiments, the semiconductor substrate 100 is a bulksemiconductor substrate, such as a semiconductor wafer. Thesemiconductor substrate 100 may include silicon or other elementarysemiconductor materials such as germanium. The semiconductor substrate100 may be un-doped or doped (e.g., p-type, n-type, or a combinationthereof). In some embodiments, the semiconductor substrate 100 includesan epitaxially grown semiconductor layer on a dielectric layer. Theepitaxially grown semiconductor layer may be made of silicon germanium,silicon, germanium, one or more other suitable materials, or acombination thereof.

In some other embodiments, the semiconductor substrate 100 includes acompound semiconductor. For example, the compound semiconductor includesone or more III-V compound semiconductors having a composition definedby the formula Al_(X1)Ga_(X2)In_(X3)As_(Y1)P_(Y2)N_(Y3)Sb_(Y4), whereX1, X2, X3, Y1, Y2, Y3, and Y4 represent relative proportions. Each ofthem is greater than or equal to zero, and added together they equal 1.The compound semiconductor may include silicon carbide, galliumarsenide, indium arsenide, indium phosphide, one or more other suitablecompound semiconductors, or a combination thereof. Other suitablesubstrate including II-VI compound semiconductors may also be used.

In some embodiments, the semiconductor substrate 100 is an active layerof a semiconductor-on-insulator (SOI) substrate. The SOI substrate maybe fabricated using a separation by implantation of oxygen (SIMOX)process, a wafer bonding process, another applicable method, or acombination thereof. In some other embodiments, the semiconductorsubstrate 100 includes a multi-layered structure. For example, thesemiconductor substrate 100 includes a silicon-germanium layer formed ona bulk silicon layer.

As shown in FIG. 2A, a semiconductor stack having multiple semiconductorlayers is formed over the semiconductor substrate 100, in accordancewith some embodiments. The semiconductor stack covers the first region10 and the second region 20 of the semiconductor substrate 10. In someembodiments, the semiconductor stack includes multiple semiconductorlayers 102 a, 102 b, 102 c, and 102 d, and the semiconductor stack alsoincludes multiple semiconductor layers 104 a, 104 b, 104 c, and 104 d.In some embodiments, the semiconductor layers 102 a-102 d and thesemiconductor layers 104 a-104 d are laid out alternately, as shown inFIG. 2A. In some embodiments, the semiconductor layer 102 a is thickerthan the semiconductor layer 102 b, 102 c, or 102 d. In someembodiments, the semiconductor layer 104 a is thicker than thesemiconductor layer 104 b, 104 c, or 104 d.

In the present disclosure, the side of the semiconductor substrate 100where the semiconductor stack is located is referred to as thefrontside. The side opposite to the frontside with respect to thesemiconductor substrate 100 is referred to as the backside.

In some embodiments, the semiconductor layers 102 b-102 d function asfirst sacrificial layers that will be removed in a subsequent process torelease the semiconductor layers 104 b-104 d. The semiconductor layers104 b-104 d that are released may function as channel structures of oneor more transistors. In some embodiments, the semiconductor layer 102 ais used as a second sacrificial layer and will be replaced with adielectric material in a subsequent process.

In some embodiments, the semiconductor layer 104 a functions as a baselayer. The base layer may be formed into base structures and be used tophysically separate a subsequently formed metal gate and a subsequentlyformed backside conductive contact from each other by a greaterdistance. Therefore, short circuiting between the subsequently formedmetal gate and the subsequently formed backside conductive contact isprevented.

In some embodiments, the semiconductor layers 104 a-104 d that will beused to form channel structures are made of a material that is differentthan that of the semiconductor layers 102 a-102 d. In some embodiments,the semiconductor layers 104 a-104 d are made of or include silicon. Insome embodiments, the first sacrificial layers (102 b-102 c) and thesecond sacrificial layer (102 a) include silicon germanium withdifferent atomic concentrations of germanium to achieve differentetching selectivity and/or different oxidation rates during subsequentprocessing.

In some embodiments, the semiconductor layer 102 a has a differentatomic concentration of germanium than that of the semiconductor layer102 b, 102 c, or 102 d. In some embodiments, the semiconductor layer 102a has a greater atomic concentration of germanium than that of thesemiconductor layer 102 b, 102 c, or 102 d. The atomic concentration ofgermanium of the semiconductor layer 102 a may be in a range from about46% to about 65%. The atomic concentration of germanium of thesemiconductor layer 102 b, 102 c, or 102 d may be in a range from about21% to about 45%.

The present disclosure contemplates that the semiconductor layers 102b-102 d, the semiconductor layers 104 a-104 d, and the semiconductorlayer 102 a include any combination of materials that can providedesired etching selectivity, desired oxidation rate differences, and/ordesired performance characteristics (e.g., materials that maximizecurrent flow).

In some embodiments, the semiconductor layers 102 a-102 d and 104 a-104d are formed using multiple epitaxial growth operations. Each of thesemiconductor layers 102 a-102 d and 104 a-104 d may be formed using aselective epitaxial growth (SEG) process, a CVD process (e.g., avapor-phase epitaxy (VPE) process, a low-pressure chemical vapordeposition (LPCVD) process, and/or an ultra-high vacuum CVD (UHV-CVD)process), a molecular beam epitaxy process, one or more other applicableprocesses, or a combination thereof. In some embodiments, thesemiconductor layers 102 a-102 d and 104 a-104 d are grown in-situ inthe same process chamber. In some embodiments, the growth of thesemiconductor layers 102 a-102 d and 104 a-104 d are alternately andsequentially performed in the same process chamber to complete theformation of the semiconductor stack. In some embodiments, the vacuum ofthe process chamber is not broken before the epitaxial growth of thesemiconductor stack is accomplished.

Afterwards, hard mask elements are formed over the semiconductor stackto assist in a subsequent patterning of the semiconductor stack. One ormore photolithography processes and one or more etching processes areused to pattern the semiconductor stack into fin structures 106A₁,106A₂, 106B₁, and 106B₂, as shown in FIG. 2B in accordance with someembodiments. The fin structures 106A₁ and 106A₂ are formed over thefirst region 10, and the fin structures 106B₁ and 106B₂ are formed overthe second region 20.

The fin structures 106A₁, 106A₂, 106B₁, and 106B₂ may be patterned byany suitable method. For example, the fin structures 106A₁, 106A₂,106B₁, and 106B₂ may be patterned using one or more photolithographyprocesses, including double-patterning or multi-patterning processes.Double-patterning or multi-patterning processes may combinephotolithography and self-aligned processes, allowing patterns to becreated that have, for example, pitches smaller than what is otherwiseobtainable using a single, direct photolithography process.

The semiconductor stack is partially removed to form trenches 112, asshown in FIG. 2B. Each of the fin structures 106A₁, 106A₂, 106B₁, and106B₂ may include portions of the semiconductor layers 102 a-102 d and104 a-104 d and semiconductor fin 101A₁, 101A₂, 101B₁ or 101B₂. Thesemiconductor substrate 100 may also be partially removed during theetching process that forms the fin structures 106A₁, 106A₂, 106B₁, and106B₂. Protruding portions of the semiconductor substrate 100 thatremain form the semiconductor fins 101A₁, 101A₂, 101B₁ and 101B₂, asshown in FIG. 2B.

Each of the hard mask elements may include a first mask layer 108 and asecond mask layer 110. The first mask layer 108 and the second masklayer 110 may be made of different materials. In some embodiments, thefirst mask layer 108 is made of a material that has good adhesion to thesemiconductor layer 104 d. The first mask layer 108 may be made ofsilicon oxide, germanium oxide, silicon germanium oxide, one or moreother suitable materials, or a combination thereof. In some embodiments,the second mask layer 110 is made of a material that has good etchingselectivity to the semiconductor layers 102 a-102 d and 104 a-104 d. Thesecond layer 110 may be made of silicon nitride, silicon oxynitride,silicon carbide, one or more other suitable materials, or a combinationthereof.

FIGS. 1A-1B are top views of various stages of a process for forming asemiconductor device structure, in accordance with some embodiments. Insome embodiments, the fin structures 106A₁, 106A₂, 106B₁ and 106B₂ areoriented lengthwise. In some embodiments, the extending directions ofthe fin structures 106A₁, 106A₂, 106B₁ and 106B₂ are substantiallyparallel to each other, as shown in FIG. 1A. In some embodiments, FIG.2B is a cross-sectional view of the structure taken along the lines2B-2B and 2B′-2B′ in FIG. 1A.

As shown in FIG. 2C, an isolation structure 114 is formed to surroundlower portions of the fin structures 106A₁, 106A₂, 106B₁ and 106B₂, inaccordance with some embodiments. In some embodiments, one or moredielectric layers are deposited over the fin structures 106A₁, 106A₂,106B₁ and 106B₂ and the semiconductor substrate 100 to overfill thetrenches 112. The dielectric layers may be made of silicon oxide,silicon oxynitride, borosilicate glass (BSG), phosphoric silicate glass(PSG), borophosphosilicate glass (BPSG), fluorinated silicate glass(FSG), low-k material, porous dielectric material, one or more othersuitable materials, or a combination thereof. The dielectric layers maybe deposited using a flowable chemical vapor deposition (FCVD) process,an atomic layer deposition (ALD) process, a chemical vapor deposition(CVD) process, one or more other applicable processes, or a combinationthereof.

Afterwards, a planarization process is used to partially remove thedielectric layers. The hard mask elements (including the first masklayer 108 and the second mask layer 110) may also function as a stoplayer of the planarization process. The planarization process mayinclude a chemical mechanical polishing (CMP) process, a grindingprocess, a dry polishing process, an etching process, one or more otherapplicable processes, or a combination thereof. Afterwards, one or moreetching back processes are used to partially remove the dielectriclayers. As a result, the remaining portion of the dielectric layersforms the isolation structure 114. Upper portions of the fin structures106A₁, 106A₂, 106B₁ and 106B₂ protrude from the top surface of theisolation structure 114, as shown in FIG. 2C.

In some embodiments, the etching back process for forming the isolationstructure 114 is carefully controlled to ensure that the topmost surfaceof the isolation structure 114 is positioned at a suitable height level,as shown in FIG. 2C. In some embodiments, the topmost surface of theisolation structure 114 is below the topmost surface of thesemiconductor layer 104 a (that functions as a base layer) and above thebottommost surface of the semiconductor layer 104 a.

Afterwards, the hard mask elements (including the first mask layer 108and the second mask layer 110) are removed. Alternatively, in some otherembodiments, the hard mask elements are removed or consumed during theplanarization process and/or the etching back process that forms theisolation structure 114.

Afterwards, dummy gate stacks 120A₁, 120A₂, 120B₁, and 120B₂ are formedto extend across the fin structures fin structures 106A₁, 106A₂, 106B₁and 106B₂, as shown in FIG. 1B in accordance with some embodiments. Insome embodiments, FIG. 2D is a cross-sectional view of the structuretaken along the lines 2D-2D and 2D′-2D′ in FIG. 1B. FIGS. 3A-3K arecross-sectional views of various stages of a process for forming asemiconductor device structure, in accordance with some embodiments. Insome embodiments, FIG. 3A is a cross-sectional view of the structuretaken along the lines 3A-3A and 3A′-3A′ in FIG. 1B.

As shown in FIGS. 1B, 2D, and 3A, the dummy gate stacks 120A₁, 120A₂,120B₁, and 120B₂ are formed to partially cover and to extend across thefin structures 106A₁, 106A₂, 106B₁ and 106B₂, in accordance with someembodiments. In some embodiments, the dummy gate stacks 120A₁ and 120A₂wraps around the fin structures 106A₁ and 106A₂. The dummy gate stacks120B₁ and 120B₂ wraps around the fin structures 106B₁ and 106B₂. Asshown in FIG. 2D, the dummy gate stack 120A₂ extends across and wrapsaround the fin structures 106A₁ and 106A₂, and the dummy gate stack120B₂ extends across and wraps around the fin structures 106B₁ and106B₂.

In some embodiments, the device formed over the second region 20 has alonger channel width than the device formed over the first region 10. Asshown in FIG. 1B, the device formed over the first region 10 has achannel width L_(SC), and the device formed over the second region 20has a channel width L_(LC). The channel width L_(LC) is longer than thechannel width L_(SC). The channel width L_(sc) may be in a range fromabout 10 nm to about 30 nm. The channel width L_(LC) may be in a rangefrom about 35 nm to about 300 nm. As shown in FIG. 1B, the pitch P_(LC)between the dummy gate stacks 120B₁ and 120B₂ is longer than the pitchP_(SC) between the dummy gate stacks 120A₁ and 120A₂.

As shown in FIGS. 2D and 3A, each of the dummy gate stacks 120A₁, 120A₂,120B₁, and 120B₂ includes a dummy gate dielectric layer 116 and a dummygate electrode 118. The dummy gate dielectric layers 116 may be made ofor include silicon oxide. The dummy gate electrodes 118 may be made ofor include polysilicon. In some embodiments, a dummy gate dielectricmaterial layer and a dummy gate electrode layer are sequentiallydeposited over the isolation feature 114 and the fin structures 106A₁,106A₂, 106B₁ and 106B₂.

The dummy gate dielectric material layer may be deposited using an ALDprocess, a CVD process, one or more other applicable processes, or acombination thereof. The dummy gate electrode layer may be depositedusing a CVD process. Afterwards, the dummy gate dielectric materiallayer and the dummy gate electrode layer are patterned to form the dummygate stacks 120A₁, 120A₂, 120B₁, and 120B₂.

In some embodiments, hard mask elements including mask layers 122 and124 are used to assist in the patterning process for forming the dummygate stacks 120A₁, 120A₂, 120B₁, and 120B₂. With the hard mask elementsas an etching mask, one or more etching processes are used to partiallyremove the dummy gate dielectric material layer and the dummy gateelectrode layer. As a result, remaining portions of the dummy gatedielectric material layer and the dummy gate electrode layer form thedummy gate stacks 120A₁, 120A₂, 120B₁, and 120B₂ that include the dummygate dielectric layer 116 and the dummy gate electrodes 118.

As shown in FIG. 3B, spacer layers 126 and 128 are afterwards depositedover the structure shown in FIG. 3A, in accordance with someembodiments. The spacer layers 126 and 128 extend along the sidewalls ofthe dummy gate stacks 120A₁, 120A₂, 120B₁, and 120B₂. The spacer layers126 and 128 are made of different materials. The spacer layer 126 may bemade of a dielectric material that has a low dielectric constant. Thespacer layer 126 may be made of or include silicon carbide, siliconoxycarbide, silicon oxide, one or more other suitable materials, or acombination thereof. The spacer layer 128 may be made of a dielectricmaterial that can provide more protection to the gate stacks duringsubsequent processes. The spacer layer 128 may have a greater dielectricconstant than that of the spacer layer 126. The spacer layer 128 may bemade of silicon nitride, silicon oxynitride, carbon-containing siliconnitride, carbon-containing silicon oxynitride, one or more othersuitable materials, or a combination thereof. The spacer layers 126 and128 may be sequentially deposited using a CVD process, an ALD process, aphysical vapor deposition (PVD) process, one or more other applicableprocesses, or a combination thereof.

As shown in FIG. 3C, the spacer layers 126 and 128 are partiallyremoved, in accordance with some embodiments. One or more anisotropicetching processes may be used to partially remove the spacer layers 126and 128. As a result, remaining portions of the spacer layers 126 and128 form gate spacers 126′ and 128′, respectively. The gate spacers 126′and 128′ extend along the sidewalls of the dummy gate stacks 120A₁,120A₂, 120B₁, and 120B₂, as shown in FIG. 3C.

In some embodiments, the fin structures 106A₁, 106A₂, 106B₁ and 106B₂are partially removed to form recesses 130 that are used to containepitaxial structures (such as source/drain structures) that will beformed later. The recesses 130 expose the side surfaces of thesemiconductor layers 102 a-102 d and 104 a-104 d. As shown in FIG. 3C,the fin structures 106A₁ and 106B₁ are partially removed to form some ofthe recesses 130, in accordance with some embodiments. One or moreetching processes may be used to form the recesses 130. In someembodiments, a dry etching process is used to form the recesses 130.Alternatively, a wet etching process may be used to form the recesses130. In some embodiments, each of the recesses 130 penetrates into thefin structure 106A₁ or 106B₁. In some embodiments, the recesses 130further extend into the semiconductor fin 101A₁ or 101B₁, as shown inFIG. 3C. In some embodiments, the gate spacers 126′ and 128′ and therecesses 130 are simultaneously formed using the same etching process.

In some embodiments, each of the recesses 130 has slanted sidewalls.Upper portions of the recesses 130 are larger (or wider) than lowerportions of the recesses 130. In these cases, due to the profile of therecesses 130, an upper semiconductor layer (such as the semiconductorlayer 104 d) is shorter than a lower semiconductor layer (such as thesemiconductor layer 104 b).

However, embodiments of the disclosure have many variations. In someother embodiments, the recesses 130 have substantially verticalsidewalls. In these cases, due to the profile of the recesses 130, anupper semiconductor layer (such as the semiconductor layer 104 d) issubstantially as wide as a lower semiconductor layer (such as thesemiconductor layer 104 b).

As shown in FIG. 3D, the semiconductor layers 102 b-102 d are laterallyetched, in accordance with some embodiments. As a result, edges of thesemiconductor layers 102 b-102 d retreat from edges of the semiconductorlayers 104 a-104 d. As shown in FIG. 3D, recesses 132 are formed due tothe lateral etching of the semiconductor layers 102 b-102 d. Therecesses 132 may be used to contain inner spacers that will be formedlater. The semiconductor layers 102 b-102 d may be laterally etchedusing a wet etching process, a dry etching process, or a combinationthereof. In some other embodiments, the semiconductor layers 102 b-102 dare partially oxidized before being laterally etched.

In some embodiments, the semiconductor layer 102 a is also etched duringthe formation of the recesses 132. As mentioned above, in someembodiments, the semiconductor layer 102 a has a greater atomicconcentration of germanium than that of the semiconductor layer 102 b,102 c, or 102 d. In some embodiments, the semiconductor layer 102 a isthicker than the semiconductor layer 102 b, 102 c, or 102 d. As aresult, the semiconductor layer 102 a is etched or oxidized at a greaterrate than the semiconductor layers 102 b-102 d.

In some embodiments, the semiconductor layers 102 a is completelyremoved during the formation the recesses 132. As a result, throughholes 302 are formed between the semiconductor fin 101A₁ and thesemiconductor layer 104 a and between the semiconductor fin 101B₁ andthe semiconductor layer 104 a, as shown in FIG. 3D in accordance withsome embodiments. Due to the support of the dummy gate stacks 120A₁,120A₂, 120B₁, and 120B₂ (as shown in FIG. 2E), the fin structure 106A₁,106A₂, 106B₁ and 106B₂ are prevented from falling down even if thesemiconductor layer 102 a is removed. The through holes 302 may be usedto contain insulating structures that will be formed later.

During the lateral etching of the semiconductor layers 102 b-102 d, thesemiconductor layers 104 a-104 d may also be slightly etched. As aresult, edge portions of the semiconductor layers 104 a-104 d arepartially etched and thus shrink to become edge elements 105 a-105 d, asshown in FIG. 3D. As shown in FIG. 3D, each of the edge elements 105a-105 d of the semiconductor layers 104 a-104 d is thinner than therespective inner portion of the semiconductor layers 104 a-104 d.

As shown in FIG. 3E, an insulating layer 134 is deposited over thestructure shown in FIG. 3D, in accordance with some embodiments. Theinsulating layer 134 covers the dummy gate stacks 120A₁, 120A₂, 120B₁,and 120B₂ and fills the recesses 132 and the through holes 302. Theinsulating layer 134 may be made of or include carbon-containing siliconnitride (SiCN), carbon-containing silicon oxynitride (SiOCN),carbon-containing silicon oxide (SiOC), silicon oxide, silicon nitride,one or more other suitable materials, or a combination thereof. In someembodiments, the insulating layer 134 is a single layer. In some otherembodiments, the insulating layer 134 includes multiple sub-layers. Someof the sub-layers may be made of different materials and/or containdifferent compositions. The insulating layer 134 may be deposited usinga CVD process, an ALD process, one or more other applicable processes,or a combination thereof.

As shown in FIG. 3F, an etching process is used to partially remove theinsulating layer 134, in accordance with some embodiments. The remainingportions of the insulating layer 134 form inner spacers 136 andinsulating structures 304, as shown in FIG. 3F. The etching process mayinclude a dry etching process, a wet etching process, or a combinationthereof.

Since the inner spacers 136 and the insulating structures 304 areportions of the insulating layer 134, the inner spacers 136 and theinsulating structures 304 are made of the same material, in accordancewith some embodiments. However, embodiments of the disclosure are notlimited thereto. In some other embodiments, the inner spacers 136 andthe insulating structures 304 are formed separately from differentinsulating layers. In these cases, the inner spacers 136 and theinsulating structures 304 may be made of different materials.

The insulating structures 304 may be made of or include a low-k material(such as silicon oxide, SiN, SiCN, SiOC, and/or SiOCN), a high-kmaterial (such as hafnium oxide, zirconium oxide, zirconium aluminumoxide, hafnium aluminum oxide, hafnium silicon oxide, and/or aluminumoxide), one or more other suitable materials (such as TiO, TaO, LaO, YO,TaCN, and/or ZrN), or a combination thereof.

The inner spacers 136 cover the edges of the semiconductor layers 102b-102 d that are originally exposed by the recesses 132. The innerspacers 136 may be used to prevent subsequently formed epitaxialstructures (that function as, for example, source/drain structures) frombeing damaged during a subsequent process for removing the sacrificiallayers 102 b-102 d. In some embodiments, the inner spacers 136 are madeof a low-k material that has a lower dielectric constant than that ofsilicon oxide. In these cases, the inner spacers 136 may also be used toreduce parasitic capacitance between the subsequently formedsource/drain structures and the gate stacks. As a result, the operationspeed of the semiconductor device structure may be improved.

In some embodiments, after the etching process for forming the innerspacers 136, portions of the semiconductor fins 101A₁ and 101B₁originally covered by the insulating layer 134 are exposed by therecesses 130, as shown in FIG. 3F. The edges of the semiconductor layers104 a-104 d are also exposed by the recesses 130, as shown in FIG. 3F.

As shown in FIG. 3G, epitaxial structures 138 are formed beside thedummy gate stacks 120A₁, 120A₂, 120B₁, and 120B₂, in accordance withsome embodiments. In some embodiments, the epitaxial structures 138 fillthe recesses 130, as shown in FIG. 3G. In some embodiments, theepitaxial structures 138 overfill the recesses 130. In these cases, thetop surfaces of the epitaxial structures 138 are higher than the topsurface of the dummy gate dielectric layer 116. In some otherembodiments, the epitaxial structures 138 partially fill the recesses130.

In some embodiments, the epitaxial structures 138 connect to thesemiconductor layers 104 b-104 d. Each of the semiconductor layers 104b-104 d is sandwiched between the epitaxial structures 138. In someembodiments, the epitaxial structures 138 function as source/drainstructures. In some embodiments, the epitaxial structures 138 are p-typedoped regions. The epitaxial structures 138 may include epitaxiallygrown silicon germanium (SiGe), epitaxially grown silicon, or anothersuitable epitaxially grown semiconductor material.

However, embodiments of the disclosure are not limited thereto. In someother embodiments, the epitaxial structures 138 are n-type dopedregions. The epitaxial structures 138 may include epitaxially grownsilicon, epitaxially grown silicon carbide (SiC), epitaxially growngermanium, or another suitable epitaxially grown semiconductor material.

In some embodiments, the epitaxial structures 138 are formed using aselective epitaxial growth (SEG) process, a CVD process (e.g., avapor-phase epitaxy (VPE) process, a low-pressure chemical vapordeposition (LPCVD) process, and/or an ultra-high vacuum CVD (UHV-CVD)process), a molecular beam epitaxy process, one or more other applicableprocesses, or a combination thereof.

In some embodiments, the epitaxial structures 138 are doped with one ormore suitable p-type dopants. For example, the epitaxial structures 138are SiGe source/drain features or Si source/drain features that aredoped with boron (B), gallium (Ga), indium (In), or another suitabledopant. In some other embodiments, the epitaxial structures 138 aredoped with one or more suitable n-type dopants. For example, theepitaxial structures 138 are Si source/drain features doped withphosphor (P), antimony (Sb), or another suitable dopant.

In some embodiments, the epitaxial structures 138 are doped in-situduring their epitaxial growth. The initial reaction gas mixture forforming the epitaxial structures 138 contains dopants. In some otherembodiments, the epitaxial structures 138 are not doped during thegrowth of the epitaxial structures 138. Instead, after the formation ofthe epitaxial structures 138, the epitaxial structures 138 are doped ina subsequent process. In some embodiments, the doping is achieved byusing an ion implantation process, a plasma immersion ion implantationprocess, a gas and/or solid source diffusion process, one or more otherapplicable processes, or a combination thereof. In some embodiments, theepitaxial structures 138 are further exposed to one or more annealingprocesses to activate the dopants. For example, a rapid thermalannealing process is used.

As shown in FIG. 3H, a contact etch stop layer 139 and a dielectriclayer 140 are formed to cover the epitaxial structures 138 and tosurround the dummy gate stacks 120A₁, 120A₂, 120B₁, and 120B₂, inaccordance with some embodiments. The contact etch stop layer 139 may bemade of or include silicon nitride, silicon oxynitride, silicon carbide,aluminum oxide, one or more other suitable materials, or a combinationthereof. The dielectric layer 140 may be made of or include siliconoxide, silicon oxynitride, borosilicate glass (BSG), phosphoric silicateglass (PSG), borophosphosilicate glass (BPSG), fluorinated silicateglass (FSG), low-k material, porous dielectric material, one or moreother suitable materials, or a combination thereof.

In some embodiments, an etch stop material layer and a dielectricmaterial layer are sequentially deposited over the structure shown inFIG. 3G. The etch stop material layer may be deposited using a CVDprocess, an ALD process, a PVD process, one or more other applicableprocesses, or a combination thereof. The dielectric material layer maybe deposited using an FCVD process, a CVD process, an ALD process, oneor more other applicable processes, or a combination thereof.

Afterwards, a planarization process is used to partially remove the etchstop material layer and the dielectric material layer. As a result, theremaining portions of the etch stop material layer and the dielectricmaterial layer respectively form the contact etch stop layer 139 and thedielectric layer 140, as shown in FIG. 3H. The planarization process mayinclude a CMP process, a grinding process, an etching process, a drypolishing process, one or more other applicable processes, or acombination thereof. In some embodiments, the mask layers 122 and 124used for defining the dummy gate stacks 120A₁, 120A₂, 120B₁, and 120B₂are also removed during the planarization process. In some embodiments,after the planarization process, the top surfaces of the contact etchstop layer 139, the dielectric layer 140, and the dummy gate electrodes118 are substantially level with each other.

As shown in FIG. 3I, protective caps 141 are formed over the dielectriclayer 140, in accordance with some embodiments. The protective caps 141may be used to protect the dielectric layer 140 thereunder. Thedielectric layer 140 may be protected during the subsequent processessuch as a subsequent metal gate etching back process. The dielectriclayer 140 may thus be kept with a suitable thickness. The protectivecaps 141 may be made of or include SiN, SiCN, SiOC, SiOCN, SiC, SiON,AlO, AlN, AlON, ZrO, ZrN, ZrAlO, HfO, one or more other suitablematerials, or a combination thereof.

In some embodiments, the dielectric layer 140 is partially removed usingone or more etching processes. As a result, recesses are formed over theremaining dielectric layer 140. Afterwards, a protective layer is formedto overfill the recesses. The protective layer may be formed using a CVDprocess, an ALD process, one or more other applicable processes, or acombination thereof. A planarization process is then used to remove theportion of the protective layer outside of the recesses. As a result,the remaining portions of the protective layer within the recesses formthe protective caps 141. The planarization process may include a CMPprocess, an etching process, a grinding process, a dry polishingprocess, one or more other applicable processes, or a combinationthereof.

As shown in FIG. 3J, one or more etching processes are used to removethe dummy gate electrodes 118 to form trenches 142, in accordance withsome embodiments. The trenches 142 are surrounded by the dielectriclayer 140. The trenches 142 expose the dummy gate dielectric layer 116.Each of the trenches 142 formed over the second region 20 is wider thaneach of the trenches 142 formed over the first region 10. During theformation of the trenches 142, the dielectric layer 140 is protected bythe protective caps 141.

As shown in FIG. 3K, the dummy gate dielectric layer 116 and thesemiconductor layers 102 b-102 d (that function as sacrificial layers)are removed, in accordance with some embodiments. In some embodiments,an etching process is used to remove the semiconductor layers 102 b-102d. As a result, recesses 144 are formed, as shown in FIG. 3K.

Due to high etching selectivity, the semiconductor layers 104 a-104 dare slightly (or substantially not) etched. The remaining portions ofthe semiconductor layers 104 b-104 d form multiple semiconductornanostructures 104 b′-104 d′ of the fin structures 106A₁ and 106B₁, asshown in FIG. 3K. The semiconductor nanostructures 104 b′-104 d′ areconstructed by or made up of the remaining portions of the semiconductorlayers 104 b-104 d. The semiconductor nanostructures 104 b′-104 d′suspended over the semiconductor fin 101A₁ or 101B₁ may function aschannel structures of transistors. In some embodiments, each of thesemiconductor nanostructures 104 b′-104 d′ formed over the second region20 is longer than each of the semiconductor nanostructures 104 b′-104 d′formed over the first region 10.

In some embodiments, the etchant used for removing the semiconductorlayers 102 b-102 d also slightly removes the semiconductor layers 104a-104 d that form the semiconductor nanostructures 104 a′-104 d′. As aresult, the obtained semiconductor nanostructures 104 a′-104 d′ becomethinner after the removal of the semiconductor layers 102 b-102 d. Asshown in FIG. 3K, each of the semiconductor nanostructures 104 b′-104 d′is thinner than the edge portions 105 b-105 d since the edge portions105 b-105 d are surrounded by other elements and thus are prevented frombeing reached and etched by the etchant, in accordance with someembodiments.

In some embodiments, due to the protection of the semiconductor layer102 b, the etchant used for removing the semiconductor layers 102 b-102d slightly (or substantially not) etches the semiconductor layer 104 a.As a result, the semiconductor layer 104 a that remains form basestructures 104 a′. In some embodiments, the base structures 104 a′ alsofunction as channel structures. In some other embodiments, the basestructures 104 a′ do not function as channel structures. The basestructures 104 a′ and the insulating structures 304 may also be used toincrease physical distance between subsequently formed metal gate stacksand backside conductive contacts (if formed). Short circuiting betweenthe metal gate stacks and the backside conductive contacts may beprevented.

After the removal of the semiconductor layers 102 b-102 d (that functionas sacrificial layers), the recesses 144 are formed. The recesses 144connect to the trench 142 and surround each of the semiconductornanostructures 104 b′-104 d′. As shown in FIG. 3K, even if the recesses144 between the semiconductor nanostructures 104 b′-104 d′ are formed,the semiconductor nanostructures 104 b′-104 d′ remain being held by theepitaxial structures 138. Therefore, after the removal of thesemiconductor layers 102 b-102 d (that function as sacrificial layers),the released semiconductor nanostructures 104 b′-104 d′ are preventedfrom falling down.

During the removal of the semiconductor layers 102 b-102 d (thatfunction as sacrificial layers), the inner spacers 136 protect theepitaxial structures 138 from being etched or damaged. The quality andreliability of the semiconductor device structure are improved. Duringthe removal of the semiconductor layers 102 b-102 d, the dielectriclayer 140 is protected by the protective caps 141, which maintains thedielectric layer 140 with a suitable thickness.

As shown in FIG. 3L, the gate spacers 126′ and 128′ are partiallyremoved, in accordance with some embodiments. Upper portions of the gatespacers 126′ and 128′ may be removed. As a result, upper portions of thetrenches 142 become wider or larger, which facilitates subsequentprocesses such as a subsequent filling process for forming metal gatestacks and a subsequent etching back process of the metal gate stacks.One or more etching processes may be used to partially remove the gatespacers 126′ and 128′.

As shown in FIG. 3M, multiple metal gate stack layers are deposited overthe structure shown in FIG. 3L, in accordance with some embodiments. Insome embodiments, the metal gate stack layers in the trenches 142 formedover the first region 10 merge together and completely fill therespective trenches 142. In some embodiments, the metal gate stacklayers partially fill the trenches 142 formed over the second region 20since the trenches 142 over the second region 20 are wider. In someembodiments, the metal gate stack layers extend into the recesses 144 towrap around each of the semiconductor nanostructures 104 b′-104 d′, asshown in FIG. 3M. In some embodiments, the metal gate stack layers overthe first region 10 and the second region 20 are simultaneously formedusing the same deposition processes. First portions of the metal gatestack layers are formed in the trenches 142 over the first region 10,and second portions of the metal gate stack layers are formed in thetrenches 142 over the second region 20.

The metal gate stack layers may include a gate dielectric layer 150, awork function layer 152, and a conductive layer 154. The conductivelayer 154 may function as a conductive filling layer that completelyfills the remaining space of the trenches 142 over the first region 10.In some embodiments, since the trenches 142 over the second region 20(i.e., a long channel region) are wider, the conductive layer 154 cannotcompletely fills the trenches 142 over the second region 20.

In some embodiments, the gate dielectric layer 150 is made of orincludes a dielectric material with high dielectric constant (high-K).The gate dielectric layer 150 may be made of or include hafnium oxide,zirconium oxide, aluminum oxide, hafnium dioxide-alumina alloy, hafniumsilicon oxide, hafnium silicon oxynitride, hafnium tantalum oxide,hafnium titanium oxide, hafnium zirconium oxide, one or more othersuitable high-K materials, or a combination thereof. The gate dielectriclayer 150 may be deposited using an ALD process, a CVD process, one ormore other applicable processes, or a combination thereof.

In some embodiments, before the formation of the gate dielectric layer150, an interfacial layers are formed on the surfaces of thesemiconductor nanostructures 104 b′-104 d′ and the base structures 104a′. The interfacial layers are very thin and are made of, for example,silicon oxide or germanium oxide. In some embodiments, the interfaciallayers are formed by applying an oxidizing agent on the surfaces of thesemiconductor nanostructures 104 b′-104 d′ and the base structures 104a′. For example, a hydrogen peroxide-containing liquid may be applied orprovided on the surfaces of the semiconductor nanostructures 104 b′-104d′ and the base structures 104 a′, so as to form the interfacial layers.

The work function layer 152 may be used to provide the desired workfunction for transistors to enhance device performance includingimproved threshold voltage. In some embodiments, the work function layer152 is used for forming a PMOS device. The work function layer 152 is ap-type work function layer. The p-type work function layer is capable ofproviding a work function value suitable for the device, such as equalto or greater than about 4.8 eV.

The p-type work function layer may include metal, metal carbide, metalnitride, other suitable materials, or a combination thereof. Forexample, the p-type metal includes tantalum nitride, tungsten nitride,titanium, titanium nitride, one or more other suitable materials, or acombination thereof.

In some other embodiments, the work function layer 152 is used forforming an NMOS device. The work function layer 152 is an n-type workfunction layer. The n-type work function layer is capable of providing awork function value suitable for the device, such as equal to or lessthan about 4.5 eV.

The n-type work function layer may include metal, metal carbide, metalnitride, or a combination thereof. For example, the n-type work functionlayer includes titanium nitride, tantalum, tantalum nitride, one or moreother suitable materials, or a combination thereof. In some embodiments,the n-type work function layer is an aluminum-containing layer. Thealuminum-containing layer may be made of or include TiAlC, TiAlO, TiAlN,one or more other suitable materials, or a combination thereof.

The work function layer 152 may also be made of or include hafnium,zirconium, titanium, tantalum, aluminum, metal carbides (e.g., hafniumcarbide, zirconium carbide, titanium carbide, aluminum carbide),aluminides, ruthenium, palladium, platinum, cobalt, nickel, conductivemetal oxides, or a combinations thereof. The thickness and/or thecompositions of the work function layer 152 may be fine-tuned to adjustthe work function level.

The work function layer 152 may be deposited over the gate dielectriclayer 150 using an ALD process, a CVD process, a PVD process, anelectroplating process, an electroless plating process, one or moreother applicable processes, or a combination thereof.

In some embodiments, a barrier layer is formed before the work functionlayer 152 to interface the gate dielectric layer 150 with thesubsequently formed work function layer 152. The barrier layer may alsobe used to prevent diffusion between the gate dielectric layer 150 andthe subsequently formed work function layer 152. The barrier layer maybe made of or include a metal-containing material. The metal-containingmaterial may include titanium nitride, tantalum nitride, one or moreother suitable materials, or a combination thereof. The barrier layermay be deposited using an ALD process, a CVD process, a PVD process, anelectroplating process, an electroless plating process, one or moreother applicable processes, or a combination thereof.

In some embodiments, the conductive layer 154 is made of or includes ametal material. The metal material may include tungsten, ruthenium,aluminum, copper, cobalt, titanium, one or more other suitablematerials, or a combination thereof. The conductive layer 154 may bedeposited over the work function layer 152 using a CVD process, an ALDprocess, a PVD process, an electroplating process, an electrolessplating process, a spin coating process, one or more other applicableprocesses, or a combination thereof.

In some embodiments, a blocking layer is formed over the work functionlayer 152 before the formation of the conductive layer 154. The blockinglayer may be used to prevent the subsequently formed conductive layer154 from diffusing or penetrating into the work function layer 152. Theblocking layer may be made of or include tantalum nitride, titaniumnitride, one or more other suitable materials, or a combination thereof.The blocking layer may be deposited using an ALD process, a PVD process,an electroplating process, an electroless plating process, one or moreother applicable processes, or a combination thereof.

In some embodiments, the conductive layer 154 does not extend into therecesses 144 since the recesses 144 are small and have been filled withother elements such as the gate dielectric layer 150 and the workfunction layer 152. However, embodiments of the disclosure are notlimited thereto. In some other embodiments, a portion of the conductivefilling extends into the recesses 144 with larger space, such as thelower recesses 144 over the second region 20.

As shown in FIG. 3N, one or more etching processes are used to partiallyremove the metal gate stack layers, in accordance with some embodiments.In some embodiments, the metal gate stack layers outside of the trenches142 are thus removed. In some embodiments, the portions of the metalgate stack layers in the trenches 142 over the second region 20 aretrimmed. As a result, the remaining portions of the metal gate stacklayers form metal gate stacks 156A₁, 156A₂, 156B₁, and 156B₂, as shownin FIG. 3N.

In some embodiments, the conductive layer 154 in the trenches 142 overthe second region 20 is partially removed from the surface of theconductive layer 154 exposed by the trenches 142 and thus becomesthinner, as shown in FIG. 3N. Due to the partial removal of the metalgate stack layers, larger space is created in the trenches 142 over thesecond region 20, which facilitates a subsequent formation of protectivestructures in the respective trenches 142.

As shown in FIG. 3N, a top portion of the metal gate stack layers in thetrench 142 over the first region 10 has a first width W_(A). A topportion of the metal gate stack layers in the trench 142 over the secondregion 20 has a second width W_(B). In some embodiments, half (i.e., thewidth W_(C)) of the first width W_(A) is greater than the second widthW_(B). Half of the first width W_(A) (i.e., the width W_(C)) may be in arange from about 5 nm to about 15 nm. The second width W_(B) may be in arange from about 3 nm to about 12 nm.

Afterwards, a protective layer is deposited over the dielectric layer140 and the metal gate stacks 156A₁, 156A₂, 156B₁, and 156B₂, inaccordance with some embodiments. The protective layer overfills thetrenches 142 over the second region 20. The protective layer may be madeof or include SiN, SiCN, SiOC, SiOCN, SiC, SiON, SiO, AlO, AlN, AlON,ZrO, ZrN, ZrAlO, HfO, one or more other suitable materials, or acombination thereof. The protective layer may be deposited using a CVDprocess, an ALD process, an FCVD process, one or more other applicableprocesses, or a combination thereof.

Afterwards, a planarization process is performed to remove the portionsof the protective layer outside of the trenches 142. As a result, theremaining portions of the protective layer form protective structures158 over the metal gate stacks 156B₁ and 156B₂, as shown in FIG. 3O inaccordance with some embodiments. The planarization process may includea CMP process, an etching process, a grinding process, a dry polishingprocess, one or more other applicable processes, or a combinationthereof. Because the conductive layer 154 of the metal gate stacks 156B₁and 156B₂ is partially removed to become thinner, more available spaceis provided for the formation of the protective structures 158. Each ofthe protective structures 158 may thus have a sufficient size andstrength to sustain the subsequent processes including a subsequentmetal gate etching back process.

As shown in FIG. 3P, the metal gate stacks 156A₁, 156A₂, 156B₁, and156B₂ are partially removed to form recesses 159A and 159B, inaccordance with some embodiments. One or more etching processes may beused to etch back the metal gate stacks 156A₁, 156A₂, 156B₁, and 156B₂.In some embodiments, after the partial removal of the metal gate stacks156A₁, 156A₂, 156B₁, and 156B₂, each of the metal gate stacks 156A₁,156A₂, 156B₁, and 156B₂ is lower than the tops of the gate spacers 126′and 128′, as shown in FIG. 3P. The tops of the gate spacers 126′ and128′ are higher than the tops of the metal gate stacks 156A₁, 156A₂,156B₁, and 156B₂. As mentioned above, each of the protective structures158 may have a sufficient size. The adhesion between the protectivestructures 158 and the neighboring elements is enhanced. The protectivestructures 158 are prevented from the peeling issue and/or the collapseissue even if the metal gate stacks 156B₁ and 156B₂ are etched back.

As shown in FIG. 3Q, protective structures 160A are formed over themetal gate stacks 156A₁ and 156A₂, and protective structures 160B areformed over the metal gate stacks 156B₁ and 156B₂, in accordance withsome embodiments. The protective structures 158, 160A, and 160B may beused to protect the metal gate stacks thereunder. The protected metalgate stacks may thus be prevented from being damaged during thesubsequent processes such as a subsequent contact formation process.

Each of the protective structures 160B extends along the sidewall of thenearby protective structure 158. In some embodiments, each of theprotective structures 160B is in direct contact with the nearbyprotective structure 158. In some embodiments, each of the protectivestructures 160B is in direct contact with the nearby protectivestructure 158, the nearby gate spacers 126′ and 128′, and the nearbymetal gate stack 156B₁ or 156B₂. In some embodiments, the bottommostsurface of the protective structure 158 is lower than the bottommostsurface of the protective structure 160B or the topmost surface of themetal gate stack 156B₁ or 156B₂.

In some embodiments, the protective structures 160A and the protectivestructures 160B are made of the same material. In some embodiments, theprotective structures 160A and the protective structures 160B are formedsimultaneously. In some other embodiments, the protective structures160A and the protective structures 160B are formed separately. In thesecases, the protective structures 160A and the protective structures 160Bmay be made of different materials. For example, the protectivestructures 160B may be made of a dielectric material that has a betterfilling ability than that of the material used for forming theprotective structures 160A. In some embodiments, the protectivestructures 160B (or 160A) and the protective structures 158 are made ofthe same material. In some other embodiments, the protective structures160B (or 160A) and the protective structures 158 are made of differentmaterials.

In some embodiments, a protective layer is deposited over the structureshown in FIG. 3O to overfill the recesses 159A and 159B, in accordancewith some embodiments. The protective layer may be made of or includeSiN, SiCN, SiOC, SiOCN, SiC, SiON, SiO, AlO, AN, AlON, ZrO, ZrN, ZrAlO,HfO, one or more other suitable materials, or a combination thereof. Theprotective layer may be deposited using a CVD process, an ALD process,an FCVD process, one or more other applicable processes, or acombination thereof.

Afterwards, a planarization process is performed to remove the portionsof the protective layer outside of the recesses 159A and 159B. As aresult, the remaining portions of the protective layer form theprotective structures 160A and 160B, as shown in FIG. 3Q in accordancewith some embodiments. The planarization process may include a CMPprocess, an etching process, a grinding process, a dry polishingprocess, one or more other applicable processes, or a combinationthereof.

As shown in FIG. 3Q, the metal gate stack 156A₁ has a width W₁. As shownin FIG. 3Q, the metal gate stack 156B₁ has a protruding portion thatextends away from the semiconductor nanostructures 104 b′-104 d′ alongthe nearby gate spacer 126′, and the portion of the metal gate stack156B₁ has a width W₂. In some embodiments, half (i.e., the width W₃) ofthe width W₁ is greater than the width W₂.

As shown in FIG. 3Q, the conductive layer 154 of the metal gate stack156A₁ or 156A₂ is thicker than the conductive layer 154 of the metalgate stack 156B₁ or 156B₂. However, embodiments of the disclosure arenot limited thereto. Many variations and/or modifications can be made toembodiments of the disclosure. For example, in some embodiments, themetal gate stacks over the first region 10 include the conductive layer154, and the metal gate stacks over the second region 10 do not includethe conductive layer 154.

FIGS. 4A-4C are cross-sectional views of various stages of a process forforming a semiconductor device structure, in accordance with someembodiments. As shown in FIG. 4A, a structure the same as or similar tothe structure shown in FIG. 3M is formed. Afterwards, similar to theembodiments illustrated in FIG. 3N, the metal gate stack layers arepartially removed. In some embodiments, the conductive layer 154originally formed over the second region 20 is completely removed, asshown in FIG. 4B. As a result, the work function layer 152 (that isoriginally covered by the conductive layer 154) is exposed.

Afterwards, the processes similar to those illustrated in FIGS. 3O-3Qare performed, in accordance with some embodiments. As a result, thestructure shown in FIG. 4C is formed. In some embodiments, theprotective structures 158 are in direct contact with the nearby workfunction layer 152.

In some embodiments, there are four channel structures (such as thesemiconductor nanostructures 104 a′-104 d′) formed. However, embodimentsof the disclosure are not limited thereto. Many variations and/ormodifications can be made to embodiments of the disclosure. In someembodiments, the total number of the semiconductor nanostructures isgreater than four. In some other embodiments, the total number of thesemiconductor nanostructures is smaller than four. The total number ofthe semiconductor nanostructures (or channel structures) of eachsemiconductor device structure may be fine-tuned to meet requirements.For example, the total number of the semiconductor nanostructures may be3 to 8. The semiconductor nanostructures may have many applicableprofiles. The semiconductor nanostructures may include nanosheets,nanowires, or other suitable nanostructures.

Embodiments of the disclosure form a semiconductor device structure witha first metal gate stack and a second metal gate stack over a shortchannel device and a long channel device, respectively. The second metalgate stack is wider than the first metal gate stack. Before forming aprotective structure over the second metal gate stack, the second metalgate stack is trimmed to be thinner to provide larger space forcontaining the protective structure. The protective structures may thushave a sufficient size to provide larger contact area with theneighboring elements. The adhesion between the protective structures andthe neighboring elements is enhanced. The protective structures may beprevented from the peeling issue and/or the collapse issue even if thesecond metal gate stack is etched back during a subsequent process. Theperformance and reliability of the semiconductor device structure arethus greatly improved.

In accordance with some embodiments, a semiconductor device structure isprovided. The semiconductor device structure includes a first channelstructure and a second channel structure over a substrate. The secondchannel structure is longer than the first channel structure. Thesemiconductor device structure also includes a first gate stack over thefirst channel structure, and the first gate stack has a first width. Thesemiconductor device structure further includes a first gate spacerextending along a sidewall of the first gate stack. In addition, thesemiconductor device structure includes a second gate stack over thesecond channel structure and a second gate spacer extending along asidewall of the second gate stack. The second gate stack has a portionextending along the second gate spacer, and the portion of the secondgate stack has a second width. Half of the first width is greater thanthe second width.

In accordance with some embodiments, a semiconductor device structure isprovided. The semiconductor device structure includes a stack of firstchannel structures and a stack of second channel structures over asubstrate. The semiconductor device structure also includes a firstmetal gate stack wrapped around the first channel structures, and thefirst metal gate stack has a first width. The semiconductor devicestructure further includes a second metal gate stack wrapped around thesecond channel structures. The second gate stack has a protrudingportion extending away from the second channel structures. Theprotruding portion of the second metal gate stack has a second width,and half of the first width is greater than the second width.

In accordance with some embodiments, a method for forming asemiconductor device structure is provided. The method includesrespectively forming a first dummy gate stack and a second dummy gatestack over a first channel structure and a second channel structure. Thesecond dummy gate stack is wider than the first dummy gate stack. Themethod also includes forming a dielectric layer to surround the firstdummy gate stack and the second dummy gate stack. The method furtherincludes removing the first dummy gate stack and the second dummy gatestack to form a first trench and a second trench. In addition, themethod includes forming metal gate stack layers with a first portion inthe first trench and a second portion in the second trench. The methodincludes trimming the second portion of the metal gate stack layers inthe second trench. The method also includes forming a protectivestructure over the second portion after the second portion is thinned.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A semiconductor device structure, comprising: afirst channel structure and a second channel structure over a substrate,wherein the second channel structure is longer than the first channelstructure; a first gate stack over the first channel structure, whereinthe first gate stack has a first width; a first gate spacer extendingalong a sidewall of the first gate stack; a second gate stack over thesecond channel structure, wherein the first gate stack has a first workfunction layer and a first conductive layer, the second gate stack has asecond work function layer and a second conductive layer, the first workfunction layer and the second work function layer are made of a samematerial, the first conductive layer and the second conductive layer aremade of a same material, and the first conductive layer is thicker thanthe second conductive layer; a second gate spacer extending along asidewall of the second gate stack, wherein the second gate stack has aportion extending along the second gate spacer, the portion of thesecond gate stack has a second width, and half of the first width isgreater than the second width; a first protective structure over thefirst gate stack, wherein a top of the first gate spacer is closer tothe substrate than a top surface of the first protective structure; anda second protective structure over the second gate stack, wherein a topof the second gate spacer is closer to the substrate than a top surfaceof the second protective structure.
 2. The semiconductor devicestructure as claimed in claim 1, wherein the top of the first gatespacer is higher than a top of the first gate stack, and the top of thesecond gate spacer is higher than a top of the second gate stack.
 3. Thesemiconductor device structure as claimed in claim 1, wherein abottommost surface of the second protective structure is lower than atopmost surface of the second gate stack.
 4. The semiconductor devicestructure as claimed in claim 1, wherein the first protective structureand the second protective structure are made of a same material.
 5. Thesemiconductor device structure as claimed in claim 1, further comprisinga third protective structure over the second gate stack, wherein thethird protective structure extends along a sidewall of the secondprotective structure.
 6. The semiconductor device structure as claimedin claim 5, wherein the first protective structure and the thirdprotective structure are made of a same material.
 7. The semiconductordevice structure as claimed in claim 5, wherein the second protectivestructure and the third protective structure are made of differentmaterials.
 8. The semiconductor device structure as claimed in claim 5,wherein the third protective structure is in direct contact with thesecond gate spacer, the second gate stack, and the second protectivestructure.
 9. The semiconductor device structure as claimed in claim 5,wherein a bottommost surface of the third protective structure is closerto the second channel structure than a bottommost surface of the secondprotective structure.
 10. The semiconductor device structure as claimedin claim 5, wherein topmost surfaces of the second protective structureand the third protective structure as substantially level with eachother.
 11. The semiconductor device structure as claimed in claim 1,wherein the second protective element is in direct contact with thesecond gate stack.
 12. A semiconductor device structure, comprising: astack of first channel structures and a stack of second channelstructures over a substrate; a first metal gate stack wrapped around thefirst channel structures, wherein the first metal gate stack has a firstwidth; a second metal gate stack wrapped around the second channelstructures, wherein the second metal gate stack has a protruding portionextending away from the second channel structures, the protrudingportion of the second metal gate stack has a second width, and half ofthe first width is greater than the second width; a first protectivestructure over the first metal gate stack; a second protective structureover the second metal gate stack; and a third protective structure overthe second metal gate stack, wherein the third protective structureextends along a sidewall of the second protective structure.
 13. Thesemiconductor device structure as claimed in claim 12, wherein the firstmetal gate stack has a first work function layer and a first conductivelayer, the second metal gate stack has a second work function layer anda second conductive layer, the first work function layer and the secondwork function layer are made of a same material, the first conductivelayer and the second conductive layer are made of a same material, andthe first conductive layer is thicker than the second conductive layer.14. The semiconductor device structure as claimed in claim 12, whereinthe first metal gate stack has a first work function layer and a firstconductive layer, the second metal gate stack has a second work functionlayer, and the first work function layer and the second work functionlayer are made of a same material.
 15. The semiconductor devicestructure as claimed in claim 14, wherein the second work function layeris in direct contact with the second protective structure.
 16. Thesemiconductor device structure as claimed in claim 12, wherein abottommost surface of the second protective structure is lower than atopmost surface of the second metal gate stack.
 17. A method for forminga semiconductor device structure, comprising: respectively forming afirst dummy gate stack and a second dummy gate stack over a firstchannel structure and a second channel structure, wherein the seconddummy gate stack is wider than the first dummy gate stack; forming adielectric layer to surround the first dummy gate stack and the seconddummy gate stack; removing the first dummy gate stack and the seconddummy gate stack to form a first trench and a second trench; formingmetal gate stack layers with a first portion in the first trench and asecond portion in the second trench; trimming the second portion of themetal gate stack layers in the second trench; forming a protectivestructure over the second portion after the second portion is thinned;etching back the first portion and the second portion of the metal gatestack layers after the protective structure is formed; forming a secondprotective structure over the first portion; and forming a thirdprotective structure over the second portion, wherein the thirdprotective structure extends along a sidewall of the protectivestructure.
 18. The method for forming a semiconductor device structureas claimed in claim 17, wherein the second protective structure and thethird protective structure are made of a same material.
 19. The methodfor forming a semiconductor device structure as claimed in claim 17,further comprising: forming a first gate spacer over a sidewall of thefirst dummy gate stack before the dielectric layer is formed; andforming a second gate spacer over a sidewall of the second dummy gatestack before the dielectric layer is formed.
 20. The method for forminga semiconductor device structure as claimed in claim 19, furthercomprising partially removing the first gate spacer and the second gatespacer after the first dummy gate stack and the second dummy gate stackare removed and before the metal gate stack layers are formed.